LOCALIZED INELASTIC FAILURE OF FLEXED PLATES: EXAMPLES FROM THE ARKOMA BASIN, USA AND CARPATHIANS FOREDEEP, POLAND

Foreland basins are typically treated as depressions formed during flexure of an elastic plate due to an end load (e.g., orogenic wedge, magmatic arc, subducting slab). However, standard models of flexural behavior do not account for localized, inelastic failure of the lithosphere as it bends (i.e. faulting and ductile deformation). Here, we present observations from two type examples of retreating collisional foreland basins that exhibit synorogenic normal faulting: the Arkoma basin, USA, and the Carpathians foredeep, Poland. In both cases, high flexural rigidity yields high magnitude normal faults (>1.5 km throw) focused in a narrow zone within the flexed plates, whereas low flexural rigidity yields lower magnitude normal faults (generally <1 km throw) distributed over broad areas. Within the Carpathian Foredeep, the high throw normal faults are clearly reactivated lithosphere scale shear zones; however, the presence of an analogous inherited structure in the Arkoma Basin remains uncertain The observed correlation between normal fault localization and magnitude, flexural rigidity, and structural inheritance provides a unique opportunity to understand the physical mechanisms responsible. We plan to utilize geodynamic simulations of lithospheric deformation to constrain lithospheric rheology and the structure of reactivated fault zones. Our preliminary modeling efforts toward this goal will utilize the open-source mantle convection and lithospheric dynamics code ASPECT to explore the relationship between tectonic compression and variable surface loading, distinct lithospheric strength profiles, and inherited fault zone architectures in controlling the development of flexurally-driven normal faulting within foreland basins. The model results will be calibrated against 1) the patterns of growth faulting and stratigraphic stacking known from subsurface modeling, and 2) the thermal history of the foredeep known from thermochronology. Models will explore specifically how lithospheric strength and the geometry of inherited weaknesses influence the development of flexural extensional faults in foreland basin settings.